You don't have to define the namespace for a basic XHTML file. In fact the namespace is assumed to be XHTML in a typical web-page file.
The part that is wrong is where you prefix every element name with html:.
Also, there were a couple of errors. You cant have height and width attributes for tables and the meta attribute charset is redundant. Spot five differences:
<?xml version="1.0" encoding="utf-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta name="generator" content= "HTML Tidy for Linux/x86 (vers 25 March 2009), see www.w3.org" /> <meta http-equiv="Content-Type" content="text/html" /> <title>Page Title</title> <meta name="keywords" content="Stuff the page is about" /> <meta name="description" content="Great little webpage" /> <script type="text/javascript"> </script> </head> <body> <table> <tr style="height:798px;"> <td></td> <td><iframe height="100%" src="CapabilitiesList.htm" width= "100%" frameborder="0" scrolling="no"></iframe></td> <td></td> </tr> </table> </body> </html>